The operation must be completed by the end of September when high seas and icy winds become a major hazard.

There are other dangers too - posed by the submarine's two nuclear reactors and its load of 24 cruise missiles, not to mention unexploded torpedoes inside the vessel and on the sea floor beside it.

The lifting operation has three main stages:

preparing the submarine for lifting

fastening cables to the hull

raising it and carrying it to a floating dock

After arrival at the scene of the disaster, the divers' first task was to remove accumulated sand and silt from the severely damaged bow.

Lift timetable

Mid-July: divers arrive

7 August: bow cut off

End August - barge sets sail

10 September: grappling starts

Mid-September: the big lift

The next priority is cutting off the submarine's nose section. The aim is to achieve this by 7 August.

The bow is so severely damaged, that it could otherwise fall off as the submarine is lifted.

If any unexploded torpedoes lie along the cutting line, they will first have to be removed. There is also a chance that the cutting operation will cause torpedoes to shift position, creating a risk of detonation.

Everything is possible, if we take into account that we are dealing with a submarine loaded with torpedoes

Russian navy chief Vladimir Kuroyedov

The cutting operation is due to be carried out by robots, using a specially designed chain saw made from a scrapped dredger.

It is considered too unsafe to allow divers in the sea at the time.

The Russian navy plans to lift the severed nose section at a later date, as part of its effort to identify the cause of the disaster.

The operation to cut 26 70cm-diameter holes through the massive structure of the hull has also begun.

Huge cables will be attached to 26 points on the hull

But this part of the plan has run into trouble. The operation commander said on 1 August that parts of the work which were supposed to be carried out by robots were having to be completed by hand.

At the end of August, or in the first days of September, an enormous barge, named Giant 4, will sail from Amsterdam.

Massive cables attached to the barge at one end, will be attached to the submarine at the 26 points where the holes were cut.

The Granit missiles are absolutely safe - all of them are in containers, which are as strong as the sub's hull

Vice-Admiral Mikhail Barskov

This grappling process is planned to begin on 10 September, with lifting beginning five or 10 days later.

In total, 23 ships will be involved in the operation, including Russian naval vessels whose goal is to ensure that prying eyes in foreign submarines do not get too close.

Radiation checks

The actual raising of the submarine - which displaces 18,300 tonnes of water - will take hydraulic lifting systems positioned along the length of the barge 12 to 15 hours to complete.

"The most risky (part) is as they lift it from the bottom, because the sea around Murmansk can be very, very rough," said an engineer with the Dutch salvage consortium, Piet Van Bruggen.

"We need to pick up some good days, and we have to be quick."

Scale models of the barge and submarine were used for laboratory tests

With the submarine clamped underneath it, the slow-moving barge will take a week to reach land, where a floating dock will be waiting at a port near Murmansk.

The remains of the 106 sailors still on board will then be removed. Bodies preserved in the cold waters of the Barents Sea will deteriorate quickly on contact with air.

Other important tasks will include the removal of 24 Granit cruise missiles situated in sturdy containers in the mid-section of the submarine.

Russian officials say that the Kursk's two nuclear reactors switched themselves off at the time of the disaster and represent no threat.